1. Field of the Invention
This invention concerns a method and apparatus for removing dissolved and suspended solids from water. It is especially directed towards a method of desalinating sea water.
2. Background of the Invention
It is known that air is saturated with water when the partial pressure of water in the air is equal to the vapor pressure at that temperature. If the partial pressure of water exceeds the vapor pressure, the air is said to be super saturated. This situation can occur when the temperature of saturated air decreases. As the temperature decreases, the relative humidity of the saturated air become greater than one-hundred percent and the super saturated air cannot hold this much water. The excess water then condenses. The temperature at which the partial pressure of water equals the vapor pressure is known as the dew point.
The principle of cooling air below its dew point has previously been employed in distilling water. For example, U.S. Pat. Nos. 4,014,751 and 4,344,826 disclose structures in which liquid is evaporated by being heated with a heating element, the evaporated liquid then being passed through a condenser to cool the vapor and collect distillate therefrom. These prior art structures have the advantage of separating water from a dissolved impurity such as salt because the heating elements evaporate only water, thereby leaving dissolved and suspended solids such as salts behind when the water vapor moves to the condenser. These prior art devices, however, require heating water with a heating element in order to evaporate the water before it reaches the cooling element. The heating and evaporating step requires substantial input of energy because of the high specific heat of water.
Since water boils at lower temperatures at lower air pressures, other prior art devices have reduced and the pressure in an evaporator to enhance the production of steam as water is heated. An example of such a method is shown in U.S. Pat. No. 3,725,206. The development and maintenance of even a partial vacuum requires specialized pumps having high energy requirements.
It is an object of the present invention to provide a more efficient method of removing dissolved and suspended solids from water by evaporating the water without applying heat from a heating element.
It is a further object of the invention to avoid the necessity for reducing air pressure to promote evaporation of the water.
It is another object of the invention to provide a compact, portable and efficient apparatus for desalinating water that is capable of being used on offshore structures such as oil platforms.